Sea-level Rise, Coastal Flooding, and Storm Events

Immediate Effects of Hurricanes on a Diverse Coral/Mangrove Ecosystem in the U.S. Virgin Islands and the Potential for Recovery

Rogers CS. Immediate Effects of Hurricanes on a Diverse Coral/Mangrove Ecosystem in the U.S. Virgin Islands and the Potential for Recovery. Diversity [Internet]. 2019 ;11(8):130. Available from: https://www.mdpi.com/1424-2818/11/8/130
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Hurricanes Irma and Maria, two powerful storms that hit the U.S. Virgin Islands less than 2 weeks apart in September 2017, caused extensive damage to the natural resources on St. John. Damage was particularly severe in a unique mangrove/coral ecosystem in three bays within Virgin Islands Coral Reef National Monument, a National Park Service marine protected area. Many Red Mangrove (Rhizophora mangle) trees were uprooted and tossed into the sea, and the prop roots of others were stripped of corals, sponges and other marine life. No other mangrove area in the Caribbean is known to have so many scleractinian corals (about 30 species before the storms). Although many corals were overturned or buried in rubble, colonies of most of the species, including four that are listed as threatened under the U.S. Endangered Species Act, survived. Recovery of this ecosystem will depend on Red Mangrove propagules becoming established and producing prop roots to support rich marine life along with a canopy to provide the shade that was critical to the biodiversity that was present before the storms. Unlike in many situations where major disturbances reduce coral cover, the substrate that must be restored for full recovery to occur is a living substrate—the prop roots of the mangroves. Larvae of corals and sponges will need to recruit on to the roots. Future storms could hinder this process.

Assessment of post-tsunami disaster land use/land cover change and potential impact of future sea-level rise to low-lying coastal areas: A case study of Banda Aceh coast of Indonesia

Meilianda E, Pradhan B, Syamsidik , Comfort LK, Alfian D, Juanda R, Syahreza S, Munadi K. Assessment of post-tsunami disaster land use/land cover change and potential impact of future sea-level rise to low-lying coastal areas: A case study of Banda Aceh coast of Indonesia. International Journal of Disaster Risk Reduction [Internet]. In Press :101292. Available from: https://www.sciencedirect.com/science/article/pii/S2212420918312524?dgcid=raven_sd_search_email
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $31.50
Type: Journal Article

The objective of this study is to investigate the impact of the projected sea-level rise to the coastal land use/land cover (LULC) at a disaster-prone coastal area, encompassing an engineering time-scale, based on a couple of sea-level rise scenarios. We investigate the Banda Aceh coast, a low-lying coastal area vulnerable to multiple hazards such as tsunamis and co-seismic land subsidence, which is typical along the Indonesian coastlines. Three sets of multi-temporal Google Earth Engine images acquired in 2004 (pre-tsunami December 2004), 2011 and 2017 were utilized to obtain the areal coverage of various types of LULC. The scenarios of coastal inundation were pre-determined at elevation +1.0 m and +1.5 m projecting the sea-level rise in the next couple centuries. Aquaculture ponds, buildings and bare land are the top three most pre-dominant land covers in Banda Aceh coast. The finding of this study reveals that the aquaculture ponds are at the highest risk to the future sea-level rise, and potentially contribute to the unproductive seawater inundated area. The bare land which has a huge potential to be converted into settlement area (buildings, housing, etc.), experienced remarkable loss due to both future inundation scenarios. The coastal area of Banda Aceh in the next couple of centuries, thus, will be highly vulnerable to the projected sea-level rise, providing the fast-growing and ever-expanding built environment very close to the coastline. A sustainable coastal management taking into account the disaster risk should, therefore, be incorporated within the decision making for the protection of the coastal area.

Sea-Level Rise and Vertical Land Motion on the Islands of Oahu and Hawaii, Hawaii

Yang L, Francis OPuananilei. Sea-Level Rise and Vertical Land Motion on the Islands of Oahu and Hawaii, Hawaii. Advances in Space Research [Internet]. In Press . Available from: https://www.sciencedirect.com/science/article/pii/S0273117719306118?dgcid=raven_sd_search_email
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $35.95
Type: Journal Article

Sea-level rise is a highly publicized issue in the Hawaiian Islands because it is one of the main drivers for coastal hazards. In our study, multiple geodetic and in situ datasets are integrated to investigate the sea-level rise and vertical land motion on the islands of Oahu and Hawaii, Hawaii. The rates of relative sea-level changes are derived from the tide-gauge stations in the Hawaiian Islands, however the station located at Kawaihae, Hawaii presents a much higher trend than other stations. Our analysis shows that the questionable trend results from the sudden movement of the equipment on land, which is caused by a pair of earthquakes. After adjustment, we arrive at a revised and more consistent relative sea-level trend at this station. Our study shows that Oahu is vertically ‘stable’ (i.e., near-zero vertical land movement within uncertainties), and the relative sea-level change is dominated by the absolute sea-level change. However, the island of Hawaii was subsiding at -3.3±0.9 mm/year before 1973 and changed to -1.2±0.2 mm/year after 1975, which may relate to seismic activities and where relative sea-level change is attributed to both absolute sea-level change and vertical land motion. The difference in relative sea-level change between the islands of Oahu and Hawaii is due to the difference in vertical land motion rather than steric sea-level change. In addition, the ocean-mass components are the predominant factors that influence the long-term trends of absolute sea level on the islands of Oahu and Hawaii.

Redating the earliest evidence of the mid-Holocene relative sea-level highstand in Australia and implications for global sea-level rise

Dougherty AJ, Thomas ZA, Fogwill C, Hogg A, Palmer J, Rainsley E, Williams AN, Ulm S, Rogers K, Jones BG, et al. Redating the earliest evidence of the mid-Holocene relative sea-level highstand in Australia and implications for global sea-level rise Riva R. PLOS ONE [Internet]. 2019 ;14(7):e0218430. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0218430
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Reconstructing past sea levels can help constrain uncertainties surrounding the rate of change, magnitude, and impacts of the projected increase through the 21st century. Of significance is the mid-Holocene relative sea-level highstand in tectonically stable and remote (far-field)locations from major ice sheets. The east coast of Australia provides an excellent arena in which to investigate changes in relative sea level during the Holocene. Considerable debate surrounds both the peak level and timing of the east coast highstand. The southeast Australian site of Bulli Beach provides the earliest evidence for the establishment of a highstand in the Southern Hemisphere, although questions have been raised about the pretreatment and type of material that was radiocarbon dated for the development of the regional sea-level curve. Here we undertake a detailed morpho- and chronostratigraphic study at Bulli Beach to better constrain the timing of the Holocene highstand in eastern Australia. In contrast to wood and charcoal samples that may provide anomalously old ages, probably due to inbuilt age, we find that short-lived terrestrial plant macrofossils provide a robust chronological framework. Bayesian modelling of the ages provide improved dating of the earliest evidence for a highstand at 6,880±50 cal BP, approximately a millennium later than previously reported. Our results from Bulli now closely align with other sea-level reconstructions along the east coast of Australia, and provide evidence for a synchronous relative sea-level highstand that extends from the Gulf of Carpentaria to Tasmania. Our refined age appears to be coincident with major ice mass loss from Northern Hemisphere and Antarctic ice sheets, supporting previous studies that suggest these may have played a role in the relative sea-level highstand. Further work is now needed to investigate the environmental impacts of regional sea levels, and refine the timing of the subsequent sea-level fall in the Holocene and its influence on coastal evolution.

Treading Water: Tools to Help US Coastal Communities Plan for Sea Level Rise Impacts

Smith EA, Sweet W, Mitchell M, Domingues R, Weaver CP, Baringer M, Goni G, Haines J, J. Loftis D, Boon J, et al. Treading Water: Tools to Help US Coastal Communities Plan for Sea Level Rise Impacts. Frontiers in Marine Science [Internet]. 2019 ;6. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2019.00300/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1023338_45_Marine_20190625_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

As communities grapple with rising seas and more frequent flooding events, they need improved projections of future rising and flooding over multiple time horizons, to assist in a multitude of planning efforts. There are currently a few different tools available that communities can use to plan, including the Sea Level Report Card and products generated by a United States. Federal interagency task force on sea level rise. These tools are a start, but it is recognized that they are not necessarily enough at present to provide communities with the type of information needed to support decisions that range from seasonal to decadal in nature, generally over relatively small geographic regions. The largest need seems to come from integrated models and tools. Agencies need to work with communities to develop tools that integrate several aspects (rainfall, tides, etc.) that affect their coastal flooding problems. They also need a formalized relationship with end users that allows agency products to be responsive to the various needs of managers and decision makers. Existing boundary organizations can be leveraged to meet this need. Focusing on addressing these needs will allow agencies to create robust solutions to flood risks, leading to truly resilient communities.

Protecting private properties from the sea: Australian policies and practice

Harvey N. Protecting private properties from the sea: Australian policies and practice. Marine Policy [Internet]. 2019 ;107:103566. Available from: https://www.sciencedirect.com/science/article/pii/S0308597X1830753X?dgcid=raven_sd_search_email
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $35.95
Type: Journal Article

The vulnerability of private coastal properties is a global issue which has arisen largely because of a lack of understanding of coastal processes. In some countries where government authorities have a long history of funding private property protection works the sustainability and ethics of policies have been questioned together with debate over public rights and the rights of property owners. In Australia, where coast protection is a responsibility of state governments there is a variation in policies and legislation relating to planning approvals for coast protection works in front of private properties. This paper examines the different Australian policies and uses examples from practice to illustrate these differences. The paper notes a wide variation in the ratio of public versus private funding which does not always match the relative proportion of benefit gained from protection works. The paper concludes that there is a complex pattern of individual state-based coastal policies, legislation and guidelines related to protection of private coastal properties. These have an underlying principle that protection works must be fully assessed in the context of effects on the adjacent coast and neighbouring properties. In reality, this requires a detailed understanding of coastal processes, particularly sediment movement, within broad sections of the coast referred to as sediment cells. Such an integrated approach has been introduced to some state-based Australian coastal legislation and strategies.

Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios

Hijuelos ACommagere, Dijkstra JT, Carruthers TJB, Heynert K, Reed DJ, van Wesenbeeck BK. Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios Chapman MGeraldine. PLOS ONE [Internet]. 2019 ;14(5):e0216695. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216695
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Understanding changes in wave attenuation by emergent vegetation as wetlands degrade or accrete over time is crucial for incorporation of wetlands into holistic coastal risk management. Linked SLAMM and XBeach models were used to investigate potential future changes in wave attenuation over a 50-year period in a degrading, subtropical wetland and a prograding, temperate wetland. These contrasting systems also have differing management contexts and were contrasted to demonstrate how the linked models can provide management-relevant insights. Morphological development of wetlands for different scenarios of sea-level rise and accretion was simulated with SLAMM and then coupled with different vegetation characteristics to predict the influence on future wave attenuation using XBeach. The geomorphological context, subsidence, and accretion resulted in large predicted reductions in the extent of vegetated land (e.g., wetland) and changes in wave height reduction potential across the wetland. These were exacerbated by increases in sea-level from +0.217 m to +0.386 m over a 50-year period, especially at the lowest accretion rates in the degrading wetland. Mangrove vegetation increased wave attenuation within the degrading, subtropical, saline wetland, while grazing reduced wave attenuation in the temperate, prograding wetland. Coastal management decisions and actions, related to coastal vegetation type and structure, have the potential to change future wave attenuation at a spatial scale relevant to coastal protection planning. Therefore, a coastal management approach that includes disaster risk reduction, biodiversity, and climate change, can be informed by coastal modeling tools, such as those demonstrated here for two contrasting case studies.

Assessing Morphologic Controls on Atoll Island Alongshore Sediment Transport Gradients Due to Future Sea-Level Rise

Shope JB, Storlazzi CD. Assessing Morphologic Controls on Atoll Island Alongshore Sediment Transport Gradients Due to Future Sea-Level Rise. Frontiers in Marine Science [Internet]. 2019 ;6. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2019.00245/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_993741_45_Marine_20190521_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Atoll islands’ alongshore sediment transport gradients depend on how island and reef morphology affect incident wave energy. It is unclear, though, how potential atoll morphologic configurations influence shoreline erosion and/or accretion patterns, and how these relationships will respond to future sea-level rise (SLR). Schematic atoll models with varying morphologies were used to evaluate the relative control of individual morphological parameters on alongshore transport gradients. Incident wave transformations were simulated using a physics-based numerical model and alongshore erosion and accretion was calculated using empirical formulae. The magnitude of the transport gradients increased with SLR: initial erosion or accretion patterns intensified. Modeled morphologic parameters that significantly influenced alongshore transport were the atoll diameter, reef flat width, reef flat depth, and island width. Modeled atolls with comparably small diameters, narrow and deep reef flats with narrow islands displayed greater magnitudes of erosion and/or accretion, especially with SLR. Windward island shorelines are projected to accrete toward the island’s longitudinal ends and lagoon due to SLR, whereas leeward islands erode along lagoon shorelines and extend toward the island ends. Oblique island, oriented parallel to the incident deepwater wave direction, shorelines are forecast to build out leeward along the reef rim and toward the lagoon while eroding along regions exposed to direct wave attack. These findings make it possible to evaluate the relative risk of alongshore erosion/accretion on atolls due to SLR in a rapid, first-order analysis.

Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios

Hijuelos ACommagere, Dijkstra JT, Carruthers TJB, Heynert K, Reed DJ, van Wesenbeeck BK. Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios Chapman MGeraldine. PLOS ONE [Internet]. 2019 ;14(5):e0216695. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216695
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Understanding changes in wave attenuation by emergent vegetation as wetlands degrade or accrete over time is crucial for incorporation of wetlands into holistic coastal risk management. Linked SLAMM and XBeach models were used to investigate potential future changes in wave attenuation over a 50-year period in a degrading, subtropical wetland and a prograding, temperate wetland. These contrasting systems also have differing management contexts and were contrasted to demonstrate how the linked models can provide management-relevant insights. Morphological development of wetlands for different scenarios of sea-level rise and accretion was simulated with SLAMM and then coupled with different vegetation characteristics to predict the influence on future wave attenuation using XBeach. The geomorphological context, subsidence, and accretion resulted in large predicted reductions in the extent of vegetated land (e.g., wetland) and changes in wave height reduction potential across the wetland. These were exacerbated by increases in sea-level from +0.217 m to +0.386 m over a 50-year period, especially at the lowest accretion rates in the degrading wetland. Mangrove vegetation increased wave attenuation within the degrading, subtropical, saline wetland, while grazing reduced wave attenuation in the temperate, prograding wetland. Coastal management decisions and actions, related to coastal vegetation type and structure, have the potential to change future wave attenuation at a spatial scale relevant to coastal protection planning. Therefore, a coastal management approach that includes disaster risk reduction, biodiversity, and climate change, can be informed by coastal modeling tools, such as those demonstrated here for two contrasting case studies.

Accounting for spatial patterns in deriving sea-level rise thresholds for salt marsh stability: More than just total areas?

Wu W. Accounting for spatial patterns in deriving sea-level rise thresholds for salt marsh stability: More than just total areas?. Ecological Indicators [Internet]. 2019 ;103:260 - 271. Available from: https://www.sciencedirect.com/science/article/pii/S2212041618305898
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $35.95
Type: Journal Article

Ecological threshold is an important concept to indicate the boundary of alternate states of ecosystems driven by environmental conditions and to facilitate evaluation of ecosystem resilience. Sea-level rise (SLR) thresholds for the stability of salt marshes, if studied in two dimensions, are generally derived based on total areas without systematic accounting for spatial patterns related to edges, shapes, and contagions of patches. As these spatial patterns are potentially important for functions and ecosystem services of salt marshes and they are likely to be impacted by SLR in a different way from the total areas, it is necessary to study SLR thresholds based on these spatial patterns to obtain a more comprehensive understanding of salt marsh resilience to SLR. This research compares the SLR thresholds based on these spatial patterns of salt marshes to those based on total areas alone across different spatial resolutions.

The spatial patterns of salt marshes were quantified by 26 commonly used landscape metrics, predicted from a mechanistic wetland change model. At spatial resolutions of 2–100 m, SLR thresholds were first derived using individual landscape metrics and then the first principal component that explained >80% of total variance of these metrics showing threshold responses to SLR. In order to separate the effect of spatial configuration from composition, a neutral model which simulated the same amount of salt marsh change as the mechanistic model but at the random locations was applied. The SLR thresholds were derived based on the simulations from the neutral model and compared to those from the mechanistic model.

The results show that total area-based SLR thresholds do not comprehensively represent salt marshes’ resilience to SLR. Particularly, I find 1) the derived SLR thresholds vary from 7.29 to 11.12 mm/yr for 2100 based on landscape metrics used, 2) the SLR threshold based on the first principal components (7.99 mm/yr) is smaller than that based on the total area only (8.40 mm/yr), 3) the SLR thresholds are scale dependent, and 4) the spatial configuration’ effect on SLR thresholds is smaller for smaller salt marsh areas compared to larger salt marsh areas.

This study highlights the need to account for different spatial patterns of salt marshes and apply wetland maps with a spatial resolutions of 30 m or finer in deriving SLR thresholds, as using total areas alone or coarser-resolution maps may provide a biased interpretation that salt marshes are more resilient to SLR than they actually are.

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